The corpses of 49 migrants who died in horrifying circumstances in the latest Mediterranean boat tragedy were delivered to Sicily on Monday in a refrigerated container.

The white metal box, stamped with the letters UN, was winched from the Norwegian ship “Siem Pilot” on to a waiting lorry at the port of Catania several hours after more than 300 survivors had disembarked.

Among those making their way tentatively down gangways on the side of the giant red vessel were a handful of women, some of them the widows of men who had perished in the broiling hold of the packed fishing boat that left Libya on Friday night.

More than 50 men were packed into the hold on departure and it quickly became unbearably hot, according to testimonies from survivors assembled by the International Organization for Migration (IOM)'s Flavio di Giacomo.

The overcrowded vessel began sinking within hours of its departure and by the time rescuers reached it 49 men had already been asphyxiated by fuel fumes filling the windowless hold.

“They had no air, no water. The heat was unbearable, especially close to the engine,” Di Giacomo told AFP.

A handful of Bangladeshi men who had been near the door of the hold had managed to escape, he added.

A total of 313 people, including at least three children, survived the sinking.

The “Siem Pilot” was also carrying 103 migrants rescued by a German ship after setting off from Libya on an overcrowded rubber dinghy.

After initial medical checks onboard, most of the rescued people were to be relocated to reception centres across Italy.

Di Giacomo said they included sub-Saharan Africans, an unusually high proportion of Moroccans and Bangladeshis.

For the dead, mainly black Africans, Bangladeshis and Pakistanis, their journey ends on Sicily's eastern shores.

Catania mayor Enzo Bianco has declared Tuesday a day of mourning and has said the city will provide space in its cemeteries for the victims to be given decent burials.

Hundreds of other migrants rescued at the weekend were disembarking at other ports across southern Italy on Monday.

Among them were 354 people, including dozens of women and children, and one corpse deposited by a Croatian patrol boat at Reggio Calabria on the toe of the Italian mainland, the coastguard said.

More than 2,300 would-be immigrants to Europe have died in the Mediterranean this year. Some 103,000 have landed in Italy and 135,000 in Greece.

Humanitarian organizations say the flux is being driven largely by conflict and repression in east Africa and the Middle East and have urged European governments to do more to create safer routes for asylum seekers to reach Europe.